Spoiler for a truck cap



FIG. 1 is a perspective view of a spoiler for a truck cap showing my new design it being understood that the broken lines are for illustrative purposes only and form no part of the claimed design;

FIG. 2 is an enlarged front elevation view thereof;

FIG. 3 is an enlarged top plan view thereof;

FIG. 4 is an enlarged rear elevation view thereof; and,

FIG. 5 is an enlarged end elevation view thereof. 

The ornamental design for a spoiler for a truck cap, as shown and described. 